1. Field of the Invention
The present invention relates to a flat particle and a process for producing the same, more particularly a flat particle composed of a base particle (A) having a functional group and an organic compound (B) having a reactive group reactive with the functional groups of said base particle (A) and which is soluble in a solvent, characterized in that at least a part of the base particle (A) and at least a part of the organic compound (B) react each other to form crosslinked structure, and a process for producing the same.
2. Description of the Prior Art
In general, a flat particle is superior to a spherical particle in hiding power, whiteness and light diffusion, and the like, and thus it has been commercialized in electric material fields including static charge developers (e.g. see Japanese Patent Application Laid-Open No. 8-202074), paint and coating materials for paper or information recording paper (e.g. see Japanese Patent Application Laid-Open No. 2-14222), adhesive agents (e.g. see Japanese Patent No. 2865534), light diffusion sheets (e.g. see Japanese Patent Application Laid-Open No. 2000-39506), etc.
Further, a flat particle furnished with a hydrophilic group has moisture retainability and absorbability and thus has been applied to various fields including fragrance, cosmetics, drug and pesticides (e.g. see Japanese Patent Nos. 2733087 and 3229011) and construction materials (e.g. see Japanese Patent No. 2918607), etc.
In general, a flat particle or a hollow particle is considered to become flat by impregnation (absorption) of a vinyl monomer including a crosslinkable monomer (a monomer having a multifunctional unsaturated double bond) into a base particle (suspension particle and emulsion particle) and thus monomer concentration in a particle is increased, which contributes generation of such a cycle as increase in polymerization rate, increase in crosslink density, shrinkage by polymerization and enhancement of layer separation by polymerization with a radical initiator.
However, a step to impregnate (absorb) a vinyl monomer including a crosslinkable monomer into a base particle must be performed in two layer region of hydrophobic region and water medium or hydrophilic medium, which requires an impregnation (absorption) step into a particle using a unit such as a high speed agitator or a homogenizer, and thus provides cost disadvantage and a problem of long processing time required.
Insufficient impregnation and absorption of a monomer into a particle or insufficient dispersion degree of a particle with an impregnated and absorbed monomer may cause a quality problem due to generation of a non-spherical particle or wider change or distribution of morphology and diameter of flat particles formed.
Therefore, objects of the present invention are, in view of the above-described problems, to provide a flat particle maintaining at least one mechanical and functional characteristics selected from reactivity, glueability and tackiness by using an organic compound other than a monomer with a double bond as a hardening agent and a crosslinking agent of a particle to make possible easy change from a base particle to a flat particle, and by adhering a residual organic compound (including a reactive group) to bond to inside and the surface of a flat particle and a method for producing the same.